Urinary incontinence (UI) affects 12% of adult females and 27% women over the age of 65 years. In the elderly 77% of incontinent women have stress urinary incontinence (SI) either alone or as a significant component of mixed incontinence. Why the prevalence of UI, and specifically SI, increases with age is not fully known nor is the pathophysiology of this common condition understood. The primary factor preventing SI is known to be an increase in the pressure closing the urethra during stress (i.e., coughing, sneezing, lifting, laughing). However, the relative contributions of the specific striated muscles, ligaments, fascias, smooth muscle and vascular structures that contribute to urethral closure during stress have not been quantified in healthy women or in women with SI. This project will address the fundamental biomechanics underlying SI and the age-associated changes that lead to its increasing prevalence. It will clarify the role that individual anatomic structures play in maintaining stress continence and their function in both young and old patients with and without SI. Detailed 3-D pelvic floor geometry and the mechanical properties of all the major passive structural tissues will be gathered from in vitro studies of 10 young and 10 old female cadaveric pelves in order to clarify the structural mechanics of the continence mechanism and structures responsible for pelvic floor integrity. Geometrical measurements will be correlated with pelvic floor MR scan data. The changes in this continence mechanism that occur with age or SI will then be quantified using in vivo studies employing fluoroscopic urodynamic and ultrasonic measures, an instrumented speculum, and myoelectric measurements. Static and dynamic characteristics of the specific anatomic structures responsible for urethral closure will be measured under relaxed and stress situations. 150 parous women ranging in age from 25-49 years will be divided into a group with SI (N=60), a group of healthy continent women (N=30), and a group of continent women with urethrocystocele (N=60) but no SI. We will examine the effects of pelvic support on each factor affecting urethral closure. To examine age effects identical studies will be performed in 150 parous women over 50 years of age. To clarify and confirm the role that each structure plays in urethral closure during resting and stress situations, biomechanical 2-D and 3-D finite element models of the urethra and pelvic floor will be developed and validated using data from the above in vitro and in vivo measurements. Sensitivity analyses will then be used to quantify, for the first time, the effects of age and the interaction between the spatiotemporal factors that affect a) pelvic floor shape and contraction state, b) vesicle neck position and shape, and c) urethral closure under varying intra-abdominal and bladder pressures. Such insights will lead to improved diagnosis and therapeutic modalities.